S H 

173 



A NEW BACTERIAL DISEASE OF FRESH -WATER 
FISHES ::::::::::: :: By H. S. Davis 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 
Document No. 024 : : : : : : : : : -: ; : ; ; : Isstied August 4, 1922 




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A NEW BACTERIAL DISEASE OF FRESH -WATER 
FISHES ::::::::::::: By H. S. Davis 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 
Document No. 924 : : : : : : : : : : : : : : : Issued August 4, 1022 




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A NEW BACTERIAL DISEASE OF FRESH-WATER FISHES. 

By H. S. DAVIS, Fish-Pathologist, V. S. Bureau of Fisheries. 

Contribution from the U. S. Fisheries Biological Station, Fairport, Iowa. 

& 

CONTENTS. 

Page. 

Introduction 261 

Description of the disease 262 

Occurrence of the disease .■ 263 

Cause of the disease 263 

Pathogenesis 265 

Methods of infection 266 

Treatment and control of the disease 2 70 

Economic importance of the disease 276 

Explanation of figures 280 

INTRODUCTION. 

While working on the protozoan parasites of fishes at the U. S. Fisheries biological 
station, Fairport, Iowa, during the summer of 191 7 a number of fish which had been 
recently placed hi aquaria were found to be dying from the effects of a bacterial infection. 
Later in the season the disease was quite prevalent among fishes confined in aquaria, 
but owing to the pressure of other work no particular attention was paid to it at that time. 

Early the following summer (1918) the disease again made its appearance, this time 
in one of the ponds. In the course of a series of feeding experiments being carried on at 
the Fairport station a large number of fingerling buffalofish were held in a pond in which 
had been placed a considerable quantity of horse manure. These fish grew rapidly for 
some time and appeared to be in a healthy, vigorous condition. However, early in 
July they began to die in large numbers, and a careful examination showed that the dying 
fish were infected with the same species of bacteria found the previous summer on fish 
in aquaria. A little later in the season the disease appeared among fishes that had 
recently been transferred to troughs for feeding experiments and caused considerable 
mortality. 

On account of its evident importance it was decided to undertake an extended 
investigation of the disease to determine, if possible, a practicable method of control. 
This investigation was begun during the latter part of the summer of 1 9 1 8 and continued 
during the summer of 1919. During, the summer of 1919 the writer was assisted by 
Miss Miriam Mackenzie. 

261 



262 BULLETIN OF THE BUREAU OP FISHERIES. 

DESCRIPTION OF THE DISEASE. 

The disease is easily recognizable, being distinguished by well-defined character- 
istics. Ordinarily the first indication of the disease is the appearance of one or more 
characteristic dirty-white or yellowish areas on some part of the body. The infected 
areas are usually quite conspicuous and increase rapidly in size. In some cases a large 
proportion of the body may eventually become infected. With the increase in the size 
of the lesions the fish become greatly weakened and usually die from 24 to 72 hours after 
the lesions first become visible. 

The lesions may occur on any part of the body, but in the majority of cases first 
appear on the fins, especially the caudals, and from there spread to adjoining portions of 
the body (figs. 23 1-237) • I n l a te stages of the disease the lesions may cover from one-half 
to two- thirds of the body, while the fins become badly frayed, the caudal sometimes be- 
coming worn to a mere stub (figs. 233 and 234). There is considerable variation in the 
site of the initial infection. As will be shown later the disease is usually the result of 
injuries and first makes its appearance in the injured region. There is also considerable 
variation dependent on the species of fish infected. In the crappies, for instance, the 
disease is usually confined to the fins and gills (figs. 231, 232, and 243) and only rarely 
does the infection spread to the body. Possibly this may be due to the fact that these 
fishes are especially susceptible to the disease and die before there is time for the bacteria 
to become widely spread over the surface of the body. 

Lesions on the gills first appear as small, white patches (figs. 243 and 244). These 
spread rapidly, and the fish usually dies within a few hours (fig. 245). 

On bullheads (Ameiurus melas and A . nebulosus) the lesions have a somewhat different 
appearance from those on scaled fishes. They usually first appear as numerous small, 
circular areas with sharp, distinct outlines (fig. 238). 

The centers of the lesions are dark blue overlaid by a whitish veil or cloudiness. 
Surrounding this is a well-defined zone about 5 mm. wide characterized by a distinctly 
reddish tinge due to hyperemia. This region, like the central portion of the lesion, is 
overlaid by a slight cloudiness. Later the lesions often become confluent and cover the 
greater portion of the body (figs. 239-241). For some reason, in fingerling bullheads 
the disease more commonly starts on the caudal fin, as in other fishes, and the infected 
area gradually advances toward the anterior end, the entire posterior end of the body be- 
coming a dirty white (fig. 242). 

In many respects the lesions resemble those produced by Saprolegnia and, in fact, 
have usually been confused with them. A careful examination will, however, readily 
enable one to distinguish between the two, since the bacterial lesions do not present the 
fuzzy appearance so characteristic of those infected with fungus. Of course they can 
easily be distinguished by a microscopical examination, but this is usually not necessary. 

In some instances a bacterial infection may be followed by an infection with Saproleg- 
nia, but in such cases the fungus is of secondary importance. During the summer very 
little fungus has been observed at Fairport and infection with Saprolegnia appears to be 
dependent on the temperature of the water. When the temperature is high (above 75 ° F.) 
the bacteria develop rapidly and the fish die SO' quickly that the fungus does not have 
time to develop to any appreciable extent. However, the bacteria are much more sus- 
ceptible to any decrease in temperature than is the Saprolegnia, the result being that 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 263 

at temperatures below 75 ° F. the bacteria develop much more slowly and the fungus 
growth may become evident before the fish succumbs. 

This is notably the case early in the fall. With the advent of cooler weather a con- 
siderable number of the diseased fish may show characteristic fungus growths in connec- 
tion with the bacterial lesions. But even in these cases there can be little doubt that the 
lesions were primarily due to bacteria and that the Saprolegnia was a secondary invader. 

Occasionally fish may die from the disease without showing any lesions on the body 
or fins. In such cases the gills are always badly infected, a large part of them being 
entirely destroyed. In late stages of gill infection the fish often show characteristic signs 
of suffocation, such as swimming at the surface and gasping for breath. In the majority 
*of cases, fish with infected gills will also show lesions on the surface of the body or fins, 
but here again there is considerable variation in different species. 

OCCURRENCE OF THE DISEASE. 

It seems probable that most species of fishes are liable to attack by this disease, 
although some species are much more susceptible than others. While it has been neces- 
sary to confine our observations to a comparatively small number of species the disease 
has been observed on the following fishes: The buffalofishes (Ictiobus bubalus and /. 
cyprinella), the sunfishes (Lepomis incisor and L. humilis), the carp (Cyprinus carpio), 
the black basses (Micropterus salmoides and M. dolomieu) , the crappies (Pomoxis spa- 
roides and P. annularis) , the warmouth {Chcsnobryttus gulosus) , the yellow perch (Perca 
flavescens) , the white bass {Roccus chrysops) , the brook trout (Salvelinus fontinalis) , the 
minnow (Pimepliales notatus), the channel catfish (Icialurus punctatus), and the bull- 
heads (Ameiurus nebulosus and A . melas) . From the above list it will be readily seen that 
the disease is widespread, and there is little reason to doubt that under favorable con- 
ditions it may occur on nearly all species of fresh-water fishes. 

In one instance several tadpoles which were confined in a tank with a number of 
infected buffalofish developed well-defined lesions on the tail. The tadpoles were just 
beginning to metamorphose, which may have made them more susceptible to infection. 
Attempts to inoculate adult frogs with the disease have proved unsuccessful. 

So far it has not been possible to obtain an)' data regarding the geographical dis- 
tribution of the disease. However, while on a visit to the St. Lawrence River at Ogdens- 
burg, N. Y., during the first week in July, 1919, the writer found the bacteria in lesions 
on the smallmouth black bass and the common perch. In this case the fish did not 
appear to be seriously injured by the bacteria which were evidently growing very slowly. 

CAUSE OF THE DISEASE. 

The disease is produced by an apparently undescribed species of bacteria for which 
I propose the name Bacillus columnaris. It has not yet been possible to grow the organ- 
ism in pure culture, but its appearance is so characteristic that it is always easily recog- 
nizable if present in any numbers. It is a long, slender, flexible, rod-shaped organism, 
5 to'12/i long and 0.5/x wide (figs. 246 and 247). The bacteria are very transparent and 
unless present in considerable numbers are difficult to distinguish on this account. 
They usually appear perfectly homogeneous, but rarely may exhibit a slightly granular 
structure. The bacteria are motile and probably possess flagella, although owing to 



264 BULLETIN OF THE BUREAU OF FISHERIES. 

lack of facilities this has not been determined with certainty. They can often be seen 
to move in a straight line for a considerable distance, the movement being accompanied 
by a sinuous bending of the rod which may temporarily assume an S-shape. One of the 
characteristic movements is to turn one end slowly in a circle, the other end remaining 
stationary and forming a pivot on which the entire rod revolves. This movement is 
very noticeable along the edge of scales or bits of infected tissue when placed on a slide. 
Large numbers of bacteria can usually be seen in such places with one end attached 
while the free end moves back and forth in the manner described above. 

Another characteristic is the formation of small chains of bacteria from one object 
to another while on the slide. The chains are formed by the bacteria arranging them- 
selves in rows joined end to end, the ends slightly overlapping. Usually these chains 
consist of two or three rows of bacteria arranged parallel to each other, but occasionally 
there may be but a single row. Bacteria can be seen continually moving back and 
forth along these living chains in a very characteristic manner. 

However, the most characteristic movement and the one which usually serves to 
make the species easily recognizable is well shown when a little material scraped from a 
lesion is placed on a slide in a drop of water. Possibly owing to the pressure of the 
cover glass the bacteria soon collect in immense numbers on the edge of bits of infected 
tissue, scales, etc. Here they form short columnlike masses, each column being sepa- 
rated a short distance from its neighbor (figs. 248 and 249). The columns usually taper 
slightly toward the free end, which is ordinarily rounded but in rare cases may be pointed. 
In some cases the ends of the columns may be distinctly enlarged. In favorable cases 
a whole series of these columns may form along the edge of a scale. These columnar 
masses of bacteria are very characteristic, and it is apparently in this way that they free 
themselves from the gelatinous matrix in which they are embedded while growing on 
the fish. Along the sides and rounded ends of the columns can be seen bacteria with 
one end attached while the free end waves back and forth in the manner already de- 
scribed. Bacteria continually break loose from the columns while others swarm out 
to take their place. Occasionally short chains may be formed extending out from the 
ends of the columns, the bacteria at the ends continually becoming free but often man- 
aging to work their way back along the chain after a time. When free, the bacteria at 
first exhibit a peculiar vibratory movement somewhat different from the Brownian 
movement and which, when once seen, is easily recognized. After being free a short 
time they usually collect on the underside of the cover glass and become perfectly 
motionless. 

These characteristic swarming movements of the bacteria are no doubt continually 
taking place on the fish, at least in late stages of the disease, for it has been found that 
badly diseased fish are continually shedding bacteria in enormous numbers. 

Owing to the fact that a variety of stains was not available the staining reactions 
of the bacteria were not studied in detail. They stain readily with f uchsin and Giemsa's 
stain, the stained preparations appearing perfectly homogeneous. 

No evidence of sporulation has been observed, and that they do not form spores 
is also indicated by the fact that the bacteria are easily killed by chemicals and drying. 

All attempts to grow the bacteria on artificial media have so far proved unsuc- 
cessful. During the summer of 19 18 the writer made several attempts to isolate the 
bacteria, and these experiments were continued by Miss Mackenzie during the summer 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 265 

of 1919. On account of the limited facilities at our disposal it was only possible to try 
a few of the simpler media. Standard beef-broth agar and fish agar were tried, and 
although bacteria appeared in the plates in large numbers no trace of columnaris could 
be found. Several lots of media with a less acid reaction than the standard were tried, 
including one with the same reaction as the river water, but the results were all nega- 
. tive. Attempts to grow the bacteria on fish serum were equally unsuccessful. Possibly 
with facilities for employing a wider range of media it may be possible to isolate the bac- 
teria. However, the failure to isolate the bacteria did not prove so serious a handicap 
in the study of the disease as would ordinarily be the case. The bacteria can easily be 
procured in large numbers from the lesions of infected fish, and their appearance is so 
characteristic that they can be readily recognized. 

While, of course, the failure to isolate the bacteria in pure culture has rendered it 
impossible to demonstrate the cause of the disease beyond question, the evidence is so 
conclusive as to leave little room for doubt. The bacteria can always be found in 
abundance in the lesions, and the disease can easily be produced in healthy fish by 
scraping off a few scales and applying a few bacteria from a diseased fish. In advanced 
stages of the disease there are usually large numbers of bacteria present in addition to 
columnaris, but it has been found that in small lesions columnaris is invariably enor- 
mously more abundant than any other organism, and in some cases when the lesions 
first become visible there is a nearly pure culture of this species present. 

Strong evidence for the causal relationship of columnaris to the disease can be seen 
in infected bullheads. The reader will recall that the lesions on these fish are charac- 
terized by an outer reddish zone about 5 mm. wide, while the center of the lesion has 
a quite different appearance. When very small the entire lesion presents the same 
appearance as the peripheral zone in later stages. As the lesions increase in size the 
characteristic blue center appears and enlarges with the growth of the lesion. It is 
obvious that the red zone is found only where the skin has been recently infected and 
that the darker color, is due to destructive changes produced by the bacteria. If a little 
material is scraped from the darker central portion of the lesion it will be found that 
considerable numbers of bacteria are present in addition to columnaris. On the other 
hand, if material from the red zone is examined it will be found that nearly all the bac- 
teria present are columnaris. Other species are so few as to be scarcely noticeable. Of 
course the same thing is true of lesions on other species of fishes, but owing to the absence 
of scales it is more striking in the case of the bullheads than elsewhere. The great 
abundance of columnaris around the advancing edge of the lesions is so noticeable that 
it soon became a matter of routine in our work to always procure the bacteria from 
this region. The smears from which the photomicrographs (figs. 246 and 247) were 
taken were made from such material. 

PATHOGENESIS. 

As previously stated the bacteria grow only on the surface of the body or on the 
gills. No case has been observed where they had penetrated any distance into the tis- 
sues. When growing on the body they destroy the integument, the muscles sometimes 
being exposed in late stages of the disease. For obvious reasons the development of 
the lesions can be more easily studied in the case of scaleless fish, such as the common 



266 BULLETIN OF THE BUREAU OF FISHERIES. 

bullhead. Figure 250 is a cross section through a lesion which is just beginning to de- 
velop. The outer layer of the epidermis has begun to disintegrate, but the inner layer 
is not yet noticeably affected. Figure 251 shows a little later stage. The epidermis 
is now entirely destroyed in one place at the right in the figure. On either side the 
epidermis is rapidly disintegrating. A somewhat later stage is shown in figure 252. 
The outer layer of the corium which has been exposed by the destruction of the epidermis . 
is now beginning to show signs of disintegration. In late stages of the disease the corium 
may be entirely destroyed in the center of the lesion, as shown in figure 253. 

As previously described, the lesion grows rapidly outward in all directions from the 
center of infection. Figures 254 to 257 are from photomicrographs of sections through 
the margins of lesions and show the disintegration of the epidermis caused by the out- 
ward growth of the bacteria. Usually there is a noticeable hyperemia just underneath 
the epidermis in this region. This is well shown in figures 255 to 257. The capillaries 
in the outer portion of the corium become gorged with blood; eventually their walls 
disintegrate and the blood fills the interstices of the corium and crowds between the 
corium and the epidermis. • Occasionally the blood corpuscles may even penetrate a 
short distance into the epidermis (fig. 255). This is the cause of the reddish zone which 
is often quite distinct around the margin. Later as the epidermis is destroyed the 
corpuscles also disintegrate. It is scarcely necessary to add that the hyperemic zone 
advances outward as the lesion enlarges. Usually the hyperemia is noticeable only 
underneath that portion of the epidermis which is undergoing disintegration, but oc- 
casionally may occur before the overlying epidermis shows any change. No case has 
been observed where the muscles showed any appreciable pathologic changes. Possibly 
this may be due to the fact that the fish usually die by the time the lesions have developed 
to the stage shown in figure 253. 

While the above account is based on a study of the lesions in bullheads the same 
conditions are found in other fishes with some slight modifications due to the presence 
of scales. In these fishes the scales become loosened and slough off as the integument 
disintegrates. 

In all cases there is a thick, matted layer of bacteria covering the lesion. This 
layer is not shown in the figures since it invariably drops off during the treatment to 
which the tissues are subjected in preparation for sectioning. Although the bacteria 
occur in enormous numbers in this superficial layer only a few scattered individuals can 
be found among the disintegrating cells of the epidermis and corium. 

When growing on the gills the bacteria produce much the same effects as on the 
integument. The epithelium and blood vessels are entirely destroyed until only the 
skeletal parts are left. As would be expected gill infections are much more quickly fatal 
than infections on the surface of the body. 

METHODS OF INFECTION. 

Since the bacteria grow only on the surface of the body and gills it is evident that 
infection can easily take place by their being carried in the water from one fish to another. 
As previously pointed out the bacteria are continually being set free from infected fish, 
especially in late stages of the disease. Where fish are crowded closely together, as in 
aquaria, the bacteria can thus readily pass from one individual to another. They are 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 267 

also easily rubbed off onto the nets or hands when diseased fish are handled and then can 
readily be transferred to healthy fish. We have several times infected healthy fish by 
simply holding them in our hands after having previously handled diseased fish. There 
is also a possibility that the disease may be transmitted by predacious insects, but no 
experiments have as yet been carried out along this line. 

Undoubtedly the most important factors in the spread of the disease under ordinary 
conditions are those which render the fish more susceptible to infection. All the evidence 
at hand indicates that the bacteria rarely or never attack healthy, uninjured fish under 
ordinary circumstances. If, however, a fish is injured or its vitality lowered in any way 
it is liable to contract the disease. Most outbreaks of the disease which have come 
under the writer's notice have occurred among fish which had been recently handled. 
As is well known it is almost impossible to handle fish without some slight injury to the 
fins or body, and even a very slight injury is all that is necessary to enable the bacteria to 
gain a foothold, and once started they are able to spread rapidly over the body. During 
warm weather, when the temperature of the water at Fairport averages about 75 to 
8o° F., an outbreak of the disease is almost certain to occur within 48 to 72 hours after 
the fish are handled. Well-defined lesions may sometimes appear in 24 hours, but the 
fish usually do not begin to die until after 48 hours. The greatest mortality usually 
occurs on the thud and fourth days, after which there is a gradual decrease until the disease 
finally disappears. If the fish are again handled, however, there is almost certain to be 
another outbreak. 

In a large percentage of cases the disease first makes its appearance on the fins, 
especially the caudal. This is, of course, readily explained since no other part of the body 
is so liable to be injured by the struggles of the fish when taken in a net. Of course, any 
slight abrasion on the surface of the body, such as the removal of a few scales or even a 
slight injury to the epithelium, is equally liable to infection. It has been found very easy 
to infect fish artificially by simply scraping away a few scales with a scalpel and applying 
a small amount of material scraped from a diseased fish. Usually a characteristic lesion 
will develop around the site of infection in 24 to 48 hours. 

There is also evidence that in some cases lowered vitality unaccompanied by me- 
chanical injuries may result in the fish becoming infected. This is probably the explana- 
tion of the epidemic which appeared in one of the ponds at Fairport in which young 
buffalofish were being held for a feeding experiment. These fish had not been handled 
for some weeks previous to the outbreak of the epidemic. Just before the disease 
appeared the water had become noticeably foul and this, no doubt, so lowered the vitality 
of the fish as to make them susceptible to infection. The writer has also been informed 
by fishermen that they had seen fish with the same disease in isolated ponds and sloughs 
along the Mississippi River late in summer. At this time the water in these ponds 
becomes very warm and stagnant, conditions which would favor the development of the 
bacteria while tending to lower the vitality of the fish. 

Another important factor influencing the spread of the disease is the temperature of 
the water. As already pointed out columnar is is very susceptible to temperature changes 
and grows rapidly only at a comparatively high temperature. The disease is distinctly 
a warm-weather disease, and so far as our observations go is not ordinarily of great 
importance when the temperature of the water is low. This was very noticeable at Fair- 
85781°— 22 2 



268 BULLETIN OP THE BUREAU OE FISHERIES. 

port during September, 1919. With the advent of cooler weather there was a consider- 
able decrease in the temperature of the water in the aquaria in which the experimental 
fish were kept. After the first week in September the average temperature of the water 
decreased from about 75 to 8o° to about 70 F. and there was a notable decrease in the 
severity of the disease. The percentage of infected fish decreased, the disease developed 
more slowly, and a considerable percentage of the infected fish recovered. 

The writer does not, however, wish to give the impression that there is no danger 
of an outbreak of the disease when the water temperature falls below 70 F. There is 
some evidence that an epidemic may occur at a comparatively low temperature, but it 
is probable that under such conditions the disease is much less severe and more easily 
controlled. That the bacteria may develop at lower temperatures is shown by an 
experiment with brook trout. A number of fingerlings were shipped to Fairport from 
the hatchery at Manchester, Iowa, and placed in a trough supplied with running water 
from a well. The temperature of the water averaged about 62 ° F. On September 13 
two badly diseased fish, one buffalofish and one bluegill, were placed in the trough among 
the trout. At a temperature of about 75 ° F. both fish would in all probability have 
died in less than 24 hours. However, after being placed in the trough with the trout 
the bluegill lived 48 hours and the buffalofish about 72 hours. One of the trout was found 
dying with the disease on September 17. Unfortunately, owing to the writer's depar- 
ture from Fairport, it was impossible to continue the experiment longer. 

During the first week in July, 1919, the writer found a slight infection on a yellow 
perch and one on a smallmouth black bass from the St. Lawrence River at Ogdensburg, 
N. Y. In each case the infection was in wounds on the side of the body. These fish 
were in a tank with a large number of other fishes, and during the three days they were 
under observation none of the other fish contracted the disease. Furthermore, the lesions 
on the infected fish did not increase noticeably in size during this time and the fish 
showed no ill effects from the disease. Since the temperature of the water averaged 
about 65 ° F. it is probable that the failure of the disease to develop rapidly and spread 
to the other fishes in the tank was largely due to this fact. Many of the other fishes 
confined in the tank had been more or less injured when captured, so there would seem 
to have been every opportunity for the disease to spread. However, in this case it was 
impossible to determine definitely whether the failure of the disease to develop was due 
to the low temperature or to the fact that the bacteria may have belonged to a much 
less virulent strain than that at Fairport. It has not yet been possible to carry out any 
detailed experiments to determine the effect of temperature on the virulence and growth 
of the bacteria, but it is hoped to do so in the near future. 

There is also evidence that, in general, fish are more likely to contract the disease 
from fish of the same species than from one of another species. This means, of course, 
that physiological strains of bacteria may be developed on different species of fish. As 
is well known such physiological strains are common among many species of bacteria. 
The strongest evidence of the occurrence of physiologically distinct strains in Bacillus, 
columnaris was obtained in the course of some experiments with the black bullhead 
(Ameiurus melas). This species is ordinarily not very susceptible to the disease, and 
during the summer of 19 19 a number of these fish were kept in the same tank with 
infected buffalofish and bluegill without any of them contracting the disease. After 
several weeks one of the bullhead was artificially inoculated with bacteria obtained 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 269 

from a diseased buffalofish. Inoculation was made as usual by scraping away the 
epidermis from a small area on one side of the body and rubbing the bacteria into the 
wound. The bullhead developed a characteristic lesion, and within 3 or 4 days practi- 
cally every bullhead in the tank became infected. The epidemic among the bullhead 
was not confined to this tank but soon spread to bullhead in adjoining tanks. This 
can be easily explained. On account of their apparent immunity to the disease no 
precautions were taken to prevent the bacteria getting from one tank to another, and 
they could easily have been transferred on the hands or nets. The epidemic developed 
with remarkable rapidity, and within a few days nearly all the bullhead which had been 
held in the tanks from one to several weeks without showing any signs of the disease 
were dead or dying. Only by the use of control measures to be described later was the 
epidemic checked and a few fish saved. It was noticeable that although the infected 
bullhead were in several instances kept in the same tanks with buffalofish and bluegill 
the disease did not spread among them nearly so rapidly as among bullhead, although 
ordinarily both buffalofish and bluegill are more susceptible to the disease. 

It has also been observed in making artificial inoculations that while it is usually 
not difficult to infect a fish with bacteria from another species a larger percentage of 
positive results is often obtained when the bacteria are taken from a fish of the same 
species. Further investigations along this line are greatly to be desired. 

As intimated above, while most species of fresh-water fishes are liable to be attacked 
by the disease some species are much more susceptible than others. It is, of course, by 
no means easy to determine accurately the relative susceptibility of different species, 
but there can be no question that there is a great deal of variation in this respect. It is 
possible to divide the fishes which have been most studied into two classes. The first 
includes those species which are very susceptible and are almost certain to contract the 
disease in large numbers if handled during warm weather. In this class we would include 
the buffalofishes (Ictiobus bubalus and cyprinella) , the crappies (Pomoxis annularis and 
sparoides), and possibly the bluegill (Lepomis incisor). The second class includes those 
fishes which are ordinarily only moderately susceptible and do not usually contract the 
disease in such numbers, even in warm weather. Furthermore, a considerable per- 
centage of the diseased fish may recover if kept under favorable conditions. In this 
class we would include the largemouth black bass (Micropterus salmoides) , the channel 
catfish (Ictalurus punctatus) , the bullheads (Ameiurus nebulosus and melas), the sunfish 
(Lepomis humilis), the carp (Cyprinus carpio), the warmouth (Chasnobryttus gulosus), 
and the white bass (Roccus chrysops). Of course it is not to be understood that all of 
the species in each class are equally susceptible, for that is certainly not the case, but in 
the present state of our knowledge it does not seem advisable to attempt a more detailed 
analysis of their relative susceptibility to the disease. 

It is also noticeable that the young of any species are, in general, more susceptible 
than are the adults. This is especially true in the case of the carp, the young of which 
are quite susceptible, while the adults are nearly immune. 

At first it was assumed that the bacteria must be widely distributed in the water, 
since this would sgiost readily explain the appearance of the disease when the fish are 
handled, but we have no proof that this is the case, and there is some evidence that the 
bacteria do not live for any length of time off the fish. If this is true, we are forced to 
assume that they are able to live in small numbers on perfectly healthy fish without 



270 BULLETIN OP THE BUREAU OF FISHERIES. 

injuring them, but are capable of increasing enormously whenever proper conditions 
arise. Such a state of affairs is not unknown as in the case of streptococci and pneu- 
mococci in man. 

TREATMENT AND CONTROL OF THE DISEASE. 

On account of the great economic importance of the disease special efforts have 
been made to develop effective methods of control. Early in the investigation it 
became evident that reliance must be placed chiefly on methods for preventing the 
spread of the disease rather than to attempt to cure fish already infected. This is due 
to the fact that the bacteria, although living exclusively on the exterior of the fish, form 
a thick, matlike growth which protects the bacteria underneath from the effects of 
chemicals. Furthermore, the bacteria soon make their way underneath the scales 
which form an additional protection. To kill bacteria in such protected situations 
requires a comparatively strong solution. 

A number of chemicals have been tried in the effort to find an effective control for 
the disease, but only potassium permanganate and copper sulphate have been found to 
be of any value. In all our experiments with chemicals we have first determined the 
maximum concentration of the chemical which the fish can stand without serious injury. 
Different species differ greatly in this respect, and unfortunately the fishes which are 
least resistant to chemicals are often very susceptible to the disease. It was soon found 
that the buffalofishes are among the most susceptible species, both to chemicals and to 
the disease, and it is believed that any treatment which will succeed with these fish will 
be equally successful with most of our common fishes. Having ascertained the strength 
of the solution which the more susceptible fishes could stand without injury, we then 
attempted to determine the minimum concentration which will kill the bacteria when 
fully exposed to the chemical. Since the bacteria can not be grown on culture media it 
is obviously impossible to determine with certainty when they are killed. It was found, 
however, that fairly accurate results could be obtained by placing the bacteria on a slide 
and then treating them with solutions of various strengths. The cessation of all move- 
ment by the bacteria was taken as evidence that they were seriously injured if not killed. 
While, of course, there are serious objections to this method it was found in practice to 
work out remarkably well. 

Of course the time element is important in the use of any chemical. Treatment 
with a very weak solution may be as effective as a much stronger solution if the time is 
sufficiently increased. Temperature may also be an important factor, but we have 
only meager data as to its effects. With few exceptions our experiments have been 
carried on with river water at a temperature of 75 to 8o° F. 

During the summer of 19 18 an extensive series of experiments with potassium 
permanganate was undertaken. It was found to greatly weaken or kill the bacteria 
in solutions so dilute that most species of fish could be kept in them for some time with- 
out serious injury. In order to kill the bacteria it is necessary to treat the fish with 
a 1 to 50,000 solution for 10 to 15 minutes. Weaker solutions have little effect. Buffalo- 
fishes can undergo this treatment without serious injury, while the black bass and sunfishes 
can stand a much stronger solution. A 1 to 20,000 solution was used on black bass 
for the same length of time with good results. However, very few fishes can stand a 
1 to 20,000 solution, and weaker solutions do not seem to penetrate far into the bacterial 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 27 1 

mat covering the lesions. Furthermore, potassium permanganate is expensive and 
dissolves slowly in water. For these reasons the potassium-permanganate treatment 
was later abandoned in favor of copper sulphate. 

A number of experiments with copper sulphate were made during the summer of 
1918, and it was found that a 1 to 30,000 solution is more effective than a 1 to 50,000 
solution of potassium permanganate and not so injurious to the fish. A solution of 
this strength will not, however, kill bacteria which are well protected, such as those 
beneath the scales. Our experiments showed that normal fingerling buffalofish are not 
appreciably injured when placed in a 1 to 30,000 solution for 30 minutes, but diseased 
or weakened fish are not so resistant. Buffalofish over 1 year old are not injured by treat- 
ment with a 1 to 25,000 solution for 30 minutes, and black bass and bullheads can 
stand a 1 to 20,000 solution for the same length of time without injury. As a result of 
these experiments the following treatment was recommended and used with much 
success : The fish previous to the appearance of any lesions are placed in a 1 to 30,000 
solution of copper sulphate for 20 minutes and are then removed at once to running 
water. If properly handled they rarely suffer any permanent injury. Wooden vessels 
are preferable, and if it is necessary to use galvanized vessels they should be painted 
to prevent chemical action between the copper sulphate and the metal sides of the vessel. 
A thin coating of melted paraffin over the inside of a galvanized tank serves the purpose 
admirably. During the treatment some of the less resistant species of fishes may swim 
around at the surface and show more or less signs of distress, but this does not neces- 
sarily indicate any serious injury. 

It should be distinctly borne in mind that the treatment to be effective must be 
given within a few hours after the fish have been handled and before any signs of infec- 
tion appear.. If the fish are to be confined in aquaria, two or three successive treat- 
ments at 12 to 24 hour intervals are advisable. When this treatment is properly used 
it is believed it will effectually prevent any serious outbreak of the disease. It must be 
repeated, however, every time the fish are handled or subjected to injury in any way. 

In an experimental test of this treatment 30 fingerling buffalofish were seined 
from one pond. They were handled quite roughly, and 14 controls were placed in a 
small aquarium without being treated. The remaining 16 fish were treated with a 1 
to 30,000 solution of copper sulphate for 20 minutes and then placed in a small aqua- 
rium like that in which the controls were held. Throughout the experiment both 
aquaria were supplied with running water, and the conditions in each were as nearly 
identical as it was possible to make them. Two of the treated fish died within 12 hours, 
probably as a result of mechanical injuries. At the end of 24 hours the fish were again 
treated with a 1 to 30,000 solution for 20 minutes. Twenty-four hours later two of the 
treated fish were found dead, but a careful examination failed to disclose any signs of 
Bacillus columnar is. Since the remaining fish showed no signs of infection no treat- 
ment was given at this time, but 6 hours later one fish showed a well-defined lesion at 
the base of the tail. This fish was at once removed and the rest given the same treat- 
ment as before. Since no further signs of infection appeared in this lot in three days 
the experiment was discontinued. 

Among the controls 3 fish showed well-defined lesions after 24 hours, and at the 
end of 48 hours 1 1 out of the 14 were dead, while 2 of the remaining 3 had well-developed 



272 BULLETIN OP THE BUREAU OP FISHERIES. 

lesions on the tail and died a few hours later. The remaining control died the next 
day with a large lesion on the side of the head. In short, there was a loss of 31 X P er 
cent among the treated fish and 100 per cent among the controls. Four of the five fish 
which died among the treated lot were in all probability killed by the direct effects of 
the copper sulphate. A large number of experiments have shown that fish when 
weakened in any way, as by handling or being kept in water deficient in oxygen, are 
much more susceptible to the injurious effects of the treatment than perfectly normal 
fish and are often killed by solutions which will not appreciably injure fish in good con- 
dition. It is this fact which has made it impossible to devise a treatment which will 
be successful under all conditions. Of course it is evident that the fish which are so 
weakened as to be injured by the treatment are the very ones which are most liable 
to contract the disease if not treated. 

It has not been practicable to conduct many experiments so completely under 
control as this one, but we have in a number of instances successfully checked by this 
treatment an outbreak of the disease among fish which were being kept in aquaria for 
other purposes. • Another test of the treatment under somewhat different conditions 
is of considerable interest: On July 20, 1919, in connection with a series of feeding 
experiments which were being carried on at the Fairport station, a number of 3-year-old 
buffalofish were seined from the pond in which they had been confined for some 
time and distributed among four different ponds. This necessitated handling the fish 
rather roughly and transferring them some distance in a galvanized tank. To make 
matters worse it was a very hot day and under ordinary circumstances there would 
undoubtedly have been considerable loss, especially since many of the fish were badly 
rubbed during the transfer. Before being liberated in the ponds all the fish were 
treated for 2o1ninutes with a 1 to 30,000 solution of copper sulphate. Of the 551 fish 
treated only 4 died as a result of the transfer, and none of these showed any evidence of 
the disease. It is unfortunate that in this case it was not practicable to keep any 
controls for comparison with the treated fish. 

While the treatment described above has been very successful it has the great 
disadvantage of requiring considerable time, and this is a serious objection where many 
fish are to be treated. During the summer of 1919 extensive experiments were carried 
on with a view to shortening the treatment. As a result a rapid treatment has been 
devised which is believed to be even more effective than the longer treatment previously 
in use. Briefly, the new method consists in treating the fish with a 1 to 1 ,000 solution 
of copper sulphate for one to two minutes. This treatment is so great an improvement 
on the earlier treatment with a 1 to 30,000 solution that in our later experiments we 
entirely discarded the latter. 

When the fish are in good condition they can be placed in the 1 to 1,000 solution 
for two minutes without injury, but if they have been previously weakened in any way 
they should not be exposed to the solution for more than one minute. Such hardy 
fishes as the black bass, sunfishes, and bullheads can be safely left in the solution for 
three minutes if in good condition. In some cases it is advisable to repeat the treatment 
after 12 to 24 hours. 

A number of experiments with the rapid treatment were carried out during the latter 
part of the summer of 1 919, but it will suffice to describe a few representative experiments. 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 



2 73 



Experiment No. 1. — September 6 a number of buffalofish and crappie were seined 
from a wire inelosure in the river (see fig. 258) where they had been held since Septem- 
ber 2. The fish were in good condition and were divided into two lots before being 
placed in aquaria well supplied with running water. Except for the copper-sulphate 
treatment both lots were kept under as nearly identical conditions as possible. Sixteen 
crappie and eight buffalofish were treated with a 1 to 1,000 solution of copper sulphate 
for two minutes (water temperature 71 F.) before being placed in the aquarium. The 
controls, 10 crappie and 8 buffalofish, were placed directly in an aquarium with- 
out treatment. September 8 among the controls there were two crappie dying with 
the disease, while most of the remaining fish showed considerable infection on the fins 
and sides of the body. Among the treated fish, one buffalofish and two crappie 
were slightly infected. At this time there was a very striking difference in appear- 
ance in the two lots of fish. The untreated fish were nearly all in bad shape, with well- 
developed lesions and considerable mucous on various parts of the body. On the other 
hand, the treated fish appeared bright and clean, and those infected showed only 
slightly developed lesions. September 9 two more crappie and one buffalofish were 
found dead among the controls. There were no new infections among the treated fish 
and one infected crappie was improving. September 10 there were one dead buffalo- 
fish and one dead crappie among the controls. The treated lot were in good con- 
dition, and those infected, with the exception of one crappie which died, were recovering. 
Since there were no new infections and the slightly infected fish in both lots were 
recovering, the experiment was discontinued on September 11. The treated lot at 
this time was noticeably in better condition than the controls. 

Summary of Experiment No. i. 





Species. 


Treated fish. 


Controls. 




Number. 


Loss from disease. 


Number. 


Loss from disease. 




16 
8 


Number. 
1 



Per cent. 


10 

8 


Number. 

5 

2 


Per cent. 


















24 


1 


4. 16 


18 


7 


38.88 





Experiment N . 2. — September 13 a number of buffalofish and crappie were removed 
from the same inelosure and treated as in the preceding experiment. Since the details 
of the experiment do not differ in principle from the preceding, it will be sufficient to 
summarize the results : 

Summary of Experiment No. 2. 





Species. 


Treated fish. 


Controls. 




Number. 


Loss from disease. 


Number. 


Loss from disease. 




3 
12 


Number. 




Per cent. 


3 

10 


Number. 
2 
5 


Per cent. 


















15 








13 


7 


53-84 





274 



BULLETIN OP THE BUREAU OP FISHERIES. 



These two experiments indicate what the copper-sulphate treatment can accom- 
plish when used under favorable conditions. If the fish have been greatly weakened 
before being given the treatment, however, the results are far from encouraging. 

As pointed out, fish which have been seriously weakened by previous treatment 
are often killed by the copper sulphate, and it is doubtful if any treatment can be 
devised which can be safely used while the fish are in this condition. This is especially 
true if the fish just previous to being treated have been confined for some time in a 
small vessel where the oxygen supply is deficient. Several experiments were carried 
out with fish seined from small ponds which had been isolated from the river when the 
waters receded after the spring floods. These fish were transported in galvanized 
wash tubs, often for a distance of 2 or 3 miles, and held in the tubs an hour or two before 
reaching the station. A large number of fish were carried in each tub, and although 
attempts were made to keep the water aerated they were partially asphyxiated when 
reaching the station. All our experiments in treating such fish were unsuccessful, the 
great majority being killed by the copper sulphate. Possibly the fish could be suc- 
cessfully treated if first held in running water for several hours. The two following 
experiments are typical of results with these exhausted fish. 

Experiment No. 3. — The fish were brought to the station at 5 p. m., September 10, 
in a greatly weakened condition. Part were treated with 1 to 1,000 copper sulphate 
for two minutes and then placed in an aquarium well supplied with running water. 
The remainder were placed in a similar aquarium without being treated. Most of the 
fish in the treated lot died within 24 hours. In the following summary all fish which 
died during the first 48 hours are tabulated as having died from the effects of the copper- 
sulphate treatment or injuries sustained on their way to the laboratory. These fish 
showed no well-developed bacterial lesions, and our previous experiments had shown 
that fish rarely die from the effects of bacteria until more than 48 hours have elapsed. 

Summary of Experiment No. 3. 





Treated fish. 


Controls. 


Species. 


Num- 
ber. 


Loss from treat- 
ment and injuries. 


Loss from disease. 


Num- 
ber. 


Loss from injuries. 


Loss from disease. 




16 
20 
3 


Number. 
11 
9 

1 


Per cent. 


Number. 





Per cent. 


21 
7 


Number. 

1 


1 


Per cent. 


Number. 
1 

5 

1 


Per cent. 
































Total 


39 


21 


S3-S4 








43 


2 


4-65 


7 


16. 27 







This case is remarkable for the small number of infected fish among the controls. 
Possibly this can be explained by the fact that although the fish had been much weak- 
ened from lack of oxygen they had evidently been handled carefully and showed only 
slight mechanical injuries. 

Experiment No. 4. — September 11 a number of buffalofish and bluegill were brought 
to the laboratory from the same pond as in the preceding experiment and were treated 
in the same way. 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 
Summary of Experiment No. 4. 



275 





Treated fish. 


Controls. 


Species. 


Num- 
ber. 


Loss from treat- 
ment and injuries. 


Loss from disease. 


Num- 
ber. 


Loss from injuries. 


Loss from disease. 




15 
9 


Number. 

10 

2 


Per cent. 


Number. 





Per cent. 


16 
10 


Number. 


1 


Per cent. 


Number. 
11 
3 


Per cent. 
























24 


12 


So 








26 


1 


3-8 5 


14 


53-S4 







As in the case of the more dilute solutions, the 1 to 1 ,000 solution of copper sulphate 
to be effective must be used before the appearance of any lesions. When the bacteria 
have become abundant enough to produce visible lesions many of them are too well 
protected to be reached by the solution during the short time the fish are exposed to it. 
However, while this treatment is not recommended as a cure, it has been shown experi- 
mentally that fish may be cured by its use, provided the gills are not infected. 

Experiment No. 5. — At 5 p. m., September 9, seven badly diseased fish, two crappie 
and five buffalofish, were treated with a 1 to 1,000 solution for two minutes. These 
fishes were so badly diseased that they would undoubtedly have died within a few hours 
if not treated. They were so weak from the disease that three buffalofish turned 
on their backs during the treatment, but two recovered later. The next morning, Sep- 
tember 10, another buffalofish was found dying and the other fish showed no improve- 
ment. The remaining fishes, two crappie and three buffalofish, were again treated with 
a 1 to 1 ,ooo solution for two minutes at 1 1 a. m. One buffalofish died shortly after treat- 
ment. At 11.30 a. m., September 11, the fish were again given a 1 to 1,000 treatment 
for two minutes. No further treatments were given, and one buffalofish and one 
crappie died on the 13th. The remaining fishes, one buffalofish and one crappie, showed 
great improvement, and on the i6th,when the experiment was discontinued, had entirely 
recovered. No doubt the relatively low temperature of the water, which averaged about 
70 F. during this experiment, was an important factor in aiding their recovery. 

Of course a longer treatment with the copper sulphate would be more destructive 
to the bacteria but would not be advisable on account of the bad effects on the fish. All 
our experiments indicate that too strong a solution or too long a treatment with a weaker 
solution is worse than no treatment at all. While the fish may not be noticeably injured 
at the time, they may be so weakened as to easily succumb to a later infection. This is 
well illustrated by one of our experiments in which five bluegill were treated with a 1 to 
1,000 solution of copper sulphate for six minutes. These fish showed no ill effects from 
the treatment at the time, but two days later all had become infected and died within 
24 hours. In another series of experiments to determine the effects of various chemicals 
six normal buffalofish were treated with a 1 to 1,000 solution of formalin for eight minutes. 
The fish appeared in good condition after the treatment, but during the next three days 
all developed a fatal case of the disease. 

In most cases it will probably not be worth while to attempt to cure fish with well- 
developed lesions, but in case it should be thought advisable the most effective treatment 
consists in local applications of a 1 per cent solution of copper sulphate. We have cured 
a number of badly diseased fish in this way, and the treatment is successful in a large 



276 BULLETIN OP THE BUREAU OP FISHERIES. 

percentage of cases, provided the gills are not affected. The solution can best be applied 
by gently swabbing the lesion with a small piece of cotton which has been previously 
dipped in the solution. Two or three applications at intervals of 6 to 12 hours 
should be sufficient. After each local application of the copper sulphate the fish should 
be placed in a 1 to 1,000 solution for one minute. 

Since, in most cases, the disease is primarily due to injuries or weakened vitality 
the old adage, "An ounce of prevention is worth a pound of cure," is peculiarly appli- 
cable in this case. Above everthing else, anyone handling fish should exercise the 
greatest care to prevent injuring the fish in any way. Even the slightest injury, such 
as the rubbing off of a few scales or even a small portion of the mucous covering, may 
lead to infection. When taken in a net or seine the delicate caudal fin is very easily 
injured by the struggles of the captured fish and every effort should be made to reduce 
the injury to a minimum. A large percentage of infections among fish taken in this way 
first appear on the caudal fin, and undoubtedly injury to the fins is one of the most 
common causes of infection. 

Great care should be taken to prevent the spread of the disease through the use 
of infected nets or vessels. This can be easily prevented, since the bacteria are entirely 
destroyed by thorough drying for several hours in direct sunlight. 

Finally, in the case of fish confined in aquaria it is essential that all infected indi- 
viduals be removed at once. As in the case of any contagious disease all contact of 
healthy with diseased individuals should be guarded against. It has been shown that 
bacteria are continually leaving diseased fish and thus may readily get on any healthy 
fish in the same aquarium. 

It should be said in passing that this treatment is also very effective for ectoparasitic 
Protozoa. Experiments on fish infected with Costia, Chilodon, and Cyclocha^ta have 
shown that these parasites are entirely destroyed by a single treatment with copper 
sulphate. In the case of fish infected with Ichthyophthirius the treatment is not so 
successful, since the encysted stages are not affected. The exposed parasites are, how- 
ever, entirely destroyed. 

A number of other chemicals have been tried, but none of them has given encour- 
aging results. Lysol and creolin were found to stop all movements of the bacteria in 
four to five minutes when diluted 1 to 5,000. The use of such strong solutions is, how- 
ever, not practicable, since buffalofish and bullheads placed in a 1 to 5,000 solution for 
1 minute died within 24 hours. Formalin was also found to be of no value for the same 
reason. 

Since sodium chloride is used a great deal by fish-culturists for fungus a number 
of infected fish were treated with solutions of various strengths. It was soon found 
that the bacteria are not appreciably affected by solutions which seriously injure the 
fish, and it is not believed that this treatment is of any value against the disease. In 
fact our experiments indicate that it may actually aggravate the disease by weakening 
the fish. 

ECONOMIC IMPORTANCE OF THE DISEASE. 

At the present time it is impossible to make any general statements regarding the 
importance of this disease. So far, with the exception of two slightly infected fish at 
Ogdensburg, N. Y., the disease has been recognized only at Fairport. Here it has caused 



BACTERIAL DISEASE OF FRESH-WATER FISHES. 277 

a very considerable mortality each summer for several years. This mortality for the 
most part has occurred in fishes which were being transferred from one pond to another, 
or to aquaria for experimental purposes. It was not until the past summer (1919) that 
the disease was shown to occur on fish in the Mississippi River as well as in the ponds. 
However, fish-culturists are well aware that is is impossible to handle many species of 
fish during warm weather with any degree of success. Undoubtedly part of this mor- 
tality among fish which have been handled is due to the direct effects of the treatment 
to which they have been subjected, but there is no question in the writer's mind that a 
much larger part is directly due to this disease and only indirectly to the handling which 
has simply rendered the fish more susceptible to infection. We are convinced that a 
great part of the mortality usually ascribed to fungus is in reality caused by Bacillus 
columnaris. In fact the writer is inclined to doubt if fungus is ever an important 'cause 
of fish mortality. In all probability Bacillus columnaris is widely distributed over the 
country and during warm weather, at least, is the most important agent in the destruc- 
tion of fish which have been injured in any way. 

Anglers are often advised to remove small fish from the hook and return them to 
the water. In the light of our experience with the disease at Fairport it is doubtful 
if many fish which have been handled in this way actually survive. Since the disease 
would not make its appearance until two or three days later, it is obvious that only 
through carefully conducted experiments can their chance of survival be ascertained. 
An incident which occurred at Fairport during the summer of 19 18 is very suggestive 
in this connection. A number of largemouth black bass were needed for some experi- 
mental work in mussel propagation. They were taken from one of the ponds on a hook 
and line and placed in a large tank supplied with running water. Within two or three 
days nearly every fish had become infected with Bacillus columnaris. As previously men- 
tioned, this species of fish is not very susceptible to the disease, and, furthermore, the 
fish in this case were several years old. As the reader will recall the older fish are much 
less susceptible than the young. 

During the last few years the Bureau of Fisheries has been rescuing large numbers 
of young fishes from the small pools and ponds in which they are imprisoned when the 
spring floods recede. These pools and ponds are widely scattered over the flood plain 
of the Mississippi, often only a few hundred yards from the river. In some instances 
they may be 2 or 3 miles from the main channel. As the waters recede these ponds 
continually grow smaller and may eventually become entirely dry. They are often 
crowded with fish and the shallow waters exposed to the hot sun of July and August 
become heated to a relatively high temperature. These conditions combined with a 
limited supply of oxygen often result in the death of large numbers of fish. The con- 
ditions are such as to render the fish susceptible to infection by Bacillus columnaris, and 
fishermen have told the writer of having seen large numbers of diseased fish in such 
ponds. 

In transferring the fish to the river they must first be seined from the ponds, a 
process which necessitates considerable rough handling, and then carried in galvanized 
washtubs (often under a broiling sun) to the river. It is obvious that such treatment 
is likely to result in infection by Bacillus columnaris. That the fish when liberated in 



278 BULLETIN OF THE BUREAU OP FISHERIES. 

the river quickly swim away and are seen no more proves nothing. The disease would 
not be evident for two or three days in any case. 

In order to determine the prevalence of the disease among rescued fishes a long 
series of experiments will be required, but owing to the limited time at the writer's 
disposal only a few preliminary experiments have as yet been carried out. In these 
experiments a special effort was made to duplicate so far as possible the average condi- 
tions found in rescue work. The fish were seined from small, isolated ponds, one of 
which is shown in figure 259, and then carried in washtubs to the river, where they were 
placed on a launch to be carried to the station. These fish were in the tubs from one-half 
to one hour, which the writer was assured by the fishermen is somewhat less than the 
average time they are held in tubs in ordinary rescue work. On reaching the station 
the fish were at once placed in an inclosure surrounded by fine-meshed poultry wire. 
This inclosure (fig. 258) was constructed in shallow water along the river shore and was 
sufficiently large to obviate any danger of the fish being crowded. A small stream 
carrying the overflow from the fishponds flowed into the inclosure, so there was a good 
supply of running water at all times. The cross partition shown in the figure was added 
later for some special experiments which are not considered in this paper. It is believed 
that the fish held in this inclosure were in fully as favorable an environment as they 
would have been if liberated in the river. 

Experiment No. 6. — September 2, 1919, 42 buffalofish, 41 crappie, and 8 bluegill 
were seined from the pond shown in figure 259. This pond was believed to be typical 
of those from which fish are taken in rescue work. It was about 400 feet long by 100 
feet wide and quite shallow, being not over 3 or 4 feet in depth at the deepest part. The 
bottom, as in most ponds of this kind, was composed of fine, soft mud. The tem- 
perature of the water at the time the fish were removed was 83° F. All the fish 
appeared in good condition when placed in the inclosure. The next day (Sept. 3) 
six crappie were found dead. Since no bacteria could be found on these fish they are 
believed to have died from injuries due to handling. September 4 one badly diseased 
buffalofish was removed, and the next day there were two dead buffalofish, both with 
well-developed lesions. The inclosure was seined on September 6 and all thefish removed. 
Only four dead fish were found, three buffalofish and one crappie. However, many of 
the living fish were badly diseased and in all probability would have died in a short time, 
but it was not thought best to leave them in the inclosure longer, since there was 
great danger of the disease spreading from the infected to the healthy fish. It is not 
believed that any of the fish which are classed as infected at this time had contracted 
the disease in this way, since all were in advanced stages of the disease. The diseased 
fishes included 1 9 buffalofish and 10 crappie. They were removed to aquaria well supplied 
with running water, but all died within 24 hours. It is believed justifiable to assume 
that all the fish classed as diseased became infected as a result of the treatment to which 
they had been subjected and would have eventually died if set free in the river. 



BACTERIAL DISEASE OE FRESH-WATER FISHES. 
Summary of Experiment No. 6. 



279 



Species. 



Number 
of fish. 



Fish lost from 
injuries. 



Fish lost from 
disease. 



Total loss of fish. 



Buffalofish 
Crappie. . . 
Bluegill. . . 



Number. 



Per cent, 
o 
14.63 



Number. 



Per cent. 
59-52 
26. S3 



Number. 

25 



Per cent. 
59.52 



Experiment No. 7. — September 6, 19 19, 36 buffalofish and 3 crappie were seined from 
the same pond as in the preceding experiment and placed in the inclosure. The next 
day eight buffalofish werefound dead, evidently from the effects of injuries due to handling. 
All the fish were removed from the inclosure on September 9. There were 17 dead 
buffalofish, 8 living badly diseased buffalofish, and 3 badly diseased crappie. The 
remaining fish were in good condition. 

Summary of Experiment No. 7. 



Species. 


Number 
of fish. 


Fish lost from 
injuries. 


Fish lost from 
disease. 


Total loss of fish. 




36 
3 


Number. 
8 



Per cent. 

22. 22 

O 


Number. 
25 

3 


Per cent. 
69.44 

TOO 


Number. 

33 

3 


Per cent. 











Experiment No. 8. — Since there was a possibility in the above experiments that the 
fish might have injured themselves on the poultry wore in trying to escape from the 
inclosure a fine-meshed seine was attached to stakes so as to form another inclosure by 
the side of the one constructed of poultry netting. September 10, 21 buffalofish and 12 
crappie were placed in this inclosure. These fish were taken from a different pond from 
that used in the preceding experiments, but conditions were much the same, except 
that the pond was somewhat farther from the station. 

Summary of Experiment No. 8. 



Species. 



Number 
of fish. 



Fish lost from 
injuries. 



Fish lost from 
disease. 



Total loss of fish. 



Buffalofish.. 
Crappie 



Per cent, 
o 
66.67 



Number. 



Per cent. 
57- 14 
16.67 



Number. 



Per cent. 
57-14 
83.33 



While the above experiments are only preliminary and too much weight should 
not be placed on the results, it is evident that the conditions are especially favorable 
for the development of this disease among rescued fish and that in all probability it 
causes a very considerable mortality during warm weather. Much of the rescue work 
is carried on in the fall and early winter, and with the low temperatures then prevailing 
there is no doubt much less danger of infection by bacteria, but on this point we have 
no data at present. 

It is obvious that great care should be exercised to injure the fish as little as pos- 
sible and that, whenever practicable, rescue operations should not be undertaken until 



280 BULLETIN OF THE BUREAU OP FISHERIES. 

cool weather. If the fish have not been greatly weakened by unfavorable conditions, 
especially lack of oxygen, treatment with i to 1,000 copper sulphate just before they are 
liberated in the river would doubtless cause a marked decrease in the loss from disease. 
Some experiments were attempted along this line in September, 1919, but owing to an 
accident the results were of no value. 

EXPLANATION OF FIGURES. 

All figures, with, the exception of figure 249, are from photographs by the author. Abbreviations 
used are as follows: bl, blood; cor, corium; ep, epidermis; and mus, muscles. 

Figs. 231 and 232. — Crappie, Pomoxis sparoides, with dorsal, caudal, and anal fins infected. Note 
lesions just starting in three places on anal fin of fish in figure 232. 

Fig. 233. — Bluegill, Lepomis incisor, with dorsal, caudal, and anal fins infected. 

Figs. 234 and 235. — Fingerling buffalofish, Ictiobus bubalus, with caudal fins badly infected. 

Fig. 236. — Largemouth black bass, Micropterus salmoides, showing infection on dorsal, anal, and 
caudal fins. 

Fig. 237. — White bass, Roccus chrysops, with infection developing on dorsal, anal, and caudal fins. 

Fig. 238. — Bullhead, Ameiurus melas, with a number of small lesions on dorsal surface of body. 

Figs. 239 and 241. — Bullheads, Ameiurus melas, in late stages of the disease. 

Fig. 240. — Bullhead, Ameiurus melas, with nearly entire side of body covered with lesions. 

Fig. 242. — Small bullhead, Ameiurus melas, with posterior end of the body infected and another 
lesion just back of pectoral fin. 

Fig. 243. — Head of crappie, Pomoxis sparoides, with operculum removed to show small lesion on 

gill. 

Fig. 244. — Head of buffalofish, Ictiobus bubalus, with operculum removed to show a somewhat larger 
lesion on gill than in figure 243. 

Fig. 245. — Head of buffalofish, Ictiobus cyprinella, with operculum removed to show gills in late 
stages of the disease. 

Figs. 246 and 247. — Bacillus columnaris . From a dried smear stained with carbolfuchsin. X 800. 

Fig. 248. — Small portion of scale of bluegill to show formation of columns by bacteria along the 
edge. Photomicrograph from preparation mounted in glycerin jelly and stained with eosin. Columns 
are more slender and pointed than normal, due to shrinkage by the preserving fluid. 

Fig. 249. — Showing formation of columns by bacteria along edge of a bit of infected tissue after 
being removed to slide. Somewhat diagrammatic. X340. 

Figs. 250 to 257 are from cross sections through lesions in integument of bullhead, Ameiurus melas. 

Fig. 250. — Lesion just beginning to develop. X 7°- 

Fig. 251. — A little later stage in development of lesion. The epidermis is entirely destroyed at 
one place to the right in the figure. X 7°. 

Fig. 252. — A somewhat later stage than figure 251. The corium is beginning to disintegrate where 
the overlying epidermis has been destroyed. X 70. 

Fig. 253. — Cross-section through lesion in late stage of disease. The corium is entirely destroyed 
at center of lesion. Less highly magnified than preceding figures. 

Fig. 254. — Showing disintegration of epidermis in early stage of development of lesion. X 108. 

Figs. 255 to 257. — Sections through margin of well-developed lesions, the epidermis at the right 
has been entirely destroyed. Note the blood corpuscles (bl) in the outer layer of the corium and between 
the corium and the epidermis. In figure 255 the blood has broken through into the epidermis for a 
short distance. X 108. 

Fig. 258. — Inclosure constructed of poultry netting in which fish were held in experiments 6, 7, 
and 8. 

Fig. 259. — Small pond from which fish were taken in experiments 6 and 7. 



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